1. Field of the Invention
This invention relates to a fuel injection control system for internal combustion engines, particularly diesel engines, and more particularly to a fuel injection control system of this kind which is provided with an actuator, such as a stepping motor, which operates to vary the delivery stroke of a plunger accommodated within each unit injector for pressure delivery of fuel, thereby controlling the amount of fuel injection.
2. Prior Art
The unit injector has an injection pump and a nozzle assembled in one body, and is capable of directly injecting an amount of fuel discharged by a plunger via the nozzle, and hence has recently come into wide use in fuel injection control systems for diesel engines. Metering means for unit injectors of this type has already been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 59-126064, which is comprised of a stepping motor provided for each unit injector for varying the delivery stroke of a plunger of the unit injector to control an amount of fuel injection by the use of a stepping motor control signal delivered from a controller to each stepping motor.
In some conventional fuel injection control systems for diesel engines, a revolution limiter is used for control of the rotational speed of the engine, in order to prevent an excessive rise in the rotational speed of the engine.
However, if such a revolution limiter is applied to the above proposed fuel injection control system, the revolution limiter cannot perform desired control before the rotational speed of the engine reaches a predetermined value. Consequently, the control of the rotational speed of the engine by the revolution limiter requires driving an actuator such as the stepping motor at an excessively high response speed after the rotational speed of the engine has reached the predetermined value, making it difficult to positively prevent an abnormal rise in the rotational speed of the engine. Further, the revolution limiter is incapable of preventing an abnormal rise in the rotational speed of the engine under all possible operating conditions of the engine.